1. Technical Field
The disclosure relates generally to integrated circuit (IC) fabrication, and more particularly, to a high dielectric constant (high-k) dielectric and metal gate stack and related methods.
2. Background Art
In the integrated circuit (IC) fabrication industry, metal gate electrodes are being pursued for, for example, the 45 nanometer (nm) and 32 nm technology nodes as a replacement for doped polysilicon (poly-Si) gate electrodes for a number of reasons. A metal gate electrode includes a high dielectric constant (high-k) dielectric within a metal gate stack. One reason, among many, that this technology is being pursued is to enable gate length scaling. Thinner gate dielectrics enable the gate length to be scaled which in turn improves the performance and density of integrated circuits. The best known self aligned process flows for complementary metal oxide semiconductor (CMOS) fabrication with the high-k dielectrics and metal gate stacks use a dual field effect transistor (FET) threshold voltage (Vt) work function tuning layers scheme to tune the threshold voltage of adjacent n-type metal oxide semiconductor (NMOS) region (for NFETs) and p-type metal oxide semiconductor (PMOS) region (for PFETs). That is, dual metal/dual dielectric gate stacks.
One challenge for this technology is that narrow width short channel transistors utilizing high-k dielectrics and metal gate electrodes in traditional CMOS gate-first processing suffer from unintentional re-growth of silicon oxide in the active regions. In particular, the high-k dielectrics such as hafnium oxide (HfO2) are deposited over a silicon active region separated by isolation regions, the latter of which typically include silicon oxide (SiO2). Consequently, the oxygen interacts with the silicon in the active region to form (re-grow) silicon oxide like dielectrics, which disadvantageously increases the equivalent oxide thickness (EOT) of the gate dielectric, i.e., the thickness of the gate dielectric is that of the high-k dielectric plus the re-grown silicon oxide in the silicon active region. This situation diminishes the goal of minimizing gate dielectric thickness. This unintentional re-growth also leads to a degradation in the ability to control when the transistor is turned on and off. The loss in control of the transistor leads to overall circuit degradation due to the large variation in turn on voltage. The large variation leads to large degradation in drive current as the width of the device decreases due to oxygen containing processes that occur after gate patterning (e.g., resist strip, rapid thermal anneal (RTA) ambients, etc). In some cases, this lateral oxidation can occur despite encapsulation.